1. Field of the Invention
The present invention relates generally to an analog-to-digital converter. More specifically, an analog-to-digital converter having reduced metastability errors is disclosed.
2. Description of Related Art
Flash analog-to-digital converter ("ADC") is often utilized in high-speed signal processing applications. Examples of such high-speed signal processing applications include hard disk drive ("HDD") read channel, digital video, instrumentation, and telecommunication. One goal for analog-to-digital converters is low error rate. Typical flash ADC architecture employs comparators coupled to thermometer-to-binary encoding logic that output the binary code digital output. Thus, reducing comparator metastability errors in high-speed ADCs is critical for achieving low error rate in the final digital output of the ADCs.
Metastability error occurs when the difference at the two inputs of a comparator is small. The comparator circuit requires a relatively long period of time to produce a well-defined logic output when the input differential is relatively small. Generally, all comparators have a small input differential voltage range for which the output does not reach the full logic level, e.g., either a logic high ("1") or a logic low ("0"), in a given clock period. Because the comparator is coupled to the downstream encoder of the ADC, the subsequent logic gates in the encoder may interpret the logic level output from the comparator at an incorrect level. Such incorrect interpretation of the comparator output often causes a gross error in the final binary code digital output.
One method for reducing metastability error is to improve the design of comparators. However, comparator requirements for low error rates often conflict with requirements for other performance metrics. Another method for reducing metastability error is to employ Gray encoding as an intermediate step to lower the probability of metastable states. However, employing the Gray encoding requires a relatively complex Gray-to-binary conversion between the thermometer and binary codes.
What is needed is a system and method to reducing metastability error in an ADC that is less complex, cost effective and easy to implement.